Troubleshooter is so overstuffed with mechanics

Every one of the hundred-plus beast-type enemies in the game unlocks three passive abilities as you level it up, which can then to taught to other beasts, and often to your human characters as well. There’s a lot of overlap—spiders tend to get abilities that interact with spiderwebs—but there’s still a huge variety of abilities in here that I haven’t unlocked elsewhere. There are even passives unlocked by monsters you can’t tame, possibly a relic of an earlier build of the game.

You can only use one monster at a time, and they don’t get leaked experience. It’s likely you’ll find one cool monster and keep using it for the rest of the game, barely interacting with this mechanic.